/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.reactive.function.server.support;

import java.util.Collections;
import java.util.List;

import reactor.core.publisher.Mono;

import org.springframework.beans.factory.InitializingBean;
import org.springframework.core.Ordered;
import org.springframework.http.codec.HttpMessageWriter;
import org.springframework.http.codec.ServerCodecConfigurer;
import org.springframework.util.Assert;
import org.springframework.util.CollectionUtils;
import org.springframework.web.reactive.HandlerResult;
import org.springframework.web.reactive.HandlerResultHandler;
import org.springframework.web.reactive.function.server.ServerResponse;
import org.springframework.web.reactive.result.view.ViewResolver;
import org.springframework.web.server.ServerWebExchange;

/**
 * {@code HandlerResultHandler} implementation that supports {@link ServerResponse}s.
 *
 * @author Arjen Poutsma
 * @since 5.0
 */
public class ServerResponseResultHandler implements HandlerResultHandler, InitializingBean, Ordered {

    private List<HttpMessageWriter<?>> messageWriters = Collections.emptyList();

    private List<ViewResolver> viewResolvers = Collections.emptyList();

    private int order = 0;


    /**
     * Configure HTTP message writers to serialize the request body with.
     * <p>By default this is set to {@link ServerCodecConfigurer}'s default writers.
     */
    public void setMessageWriters(List<HttpMessageWriter<?>> configurer) {
        Assert.notNull(messageWriters, "'messageWriters' must not be null");
        this.messageWriters = configurer;
    }

    public void setViewResolvers(List<ViewResolver> viewResolvers) {
        this.viewResolvers = viewResolvers;
    }

    /**
     * Set the order for this result handler relative to others.
     * <p>By default set to 0. It is generally safe to place it early in the
     * order as it looks for a concrete return type.
     *
     * @param order the order
     */
    public void setOrder(int order) {
        this.order = order;
    }

    @Override
    public int getOrder() {
        return this.order;
    }


    @Override
    public void afterPropertiesSet() throws Exception {
        if (CollectionUtils.isEmpty(this.messageWriters)) {
            throw new IllegalArgumentException("Property 'messageWriters' is required");
        }
    }

    @Override
    public boolean supports(HandlerResult result) {
        return (result.getReturnValue() instanceof ServerResponse);
    }

    @Override
    public Mono<Void> handleResult(ServerWebExchange exchange, HandlerResult result) {
        ServerResponse response = (ServerResponse) result.getReturnValue();
        Assert.state(response != null, "No ServerResponse");
        return response.writeTo(exchange, new ServerResponse.Context() {
            @Override
            public List<HttpMessageWriter<?>> messageWriters() {
                return messageWriters;
            }

            @Override
            public List<ViewResolver> viewResolvers() {
                return viewResolvers;
            }
        });
    }
}
